Georgia cotton growers seeing insect resurgence

Georgia cotton insects staged a revival of sorts in 2002, with growers seeing more pressure and activity since 1997, says Phillip Roberts, University of Georgia Extension entomologist.

“We did see somewhat of a resurgence in numbers this past year,” said Roberts at the recent Georgia Cotton Production Workshop in Tifton. “Growers in some areas had very difficult situations, but we were able to handle most of the insect pressure.”

Was 2002 a bad insect year on Georgia cotton? “If we look at the number of insecticide sprays on non-Bt cotton this year and compare it to the number of sprays we were making in the mid-1990s — before the advent of Bt cotton — it doesn't look so bad. Maybe this past year was normal,” says Roberts.

A survey of county Extension agents from this past year showed that Georgia growers sprayed an average of four to four and a half times on non-Bt cotton, he says. “A larger number of sprays were being made on non-Bt cotton depending on where you were located. We still have some non-Bt cotton being grown without insecticides. But in some areas, growers had to make nine to 10 sprays. That was in very difficult situations.”

The statewide range of sprays on Bt cotton was from zero to three or four, he adds.

Insect scouting will be a “must” in 2003, contends Roberts. “The number of acres we're scouting on a consistent basis has decreased in recent years, and maybe more so on Bollgard or Bt cotton than on conventional cotton.

“Scouting twice a week is a must on conventional or non-Bt cotton, and once a week is unacceptable on non-Bt cotton. You potentially could get into some serious trouble. It takes three days for a tobacco budworm to hatch. In a week's time, you can go from nothing to an insect that's beginning to get too large for us to do our best with insecticides,” he says.

Once a week scouting probably is acceptable on Bt cotton, says Roberts. “We'd prefer twice a week, but once a week appears to be working on Bt cotton.”

It's also important, he continues, that good, experienced consultants or scouts are looking at cotton. “You need someone with experience scouting cotton to help maximize your profits. We have to understand our system. We're trying to manage bugs and worms. And, as we saw this year, insecticide selection has become even more important as we try to manage tobacco budworms. Expertise has value, and a good scout is money well spent.”

Georgia growers must manage tobacco budworms and corn earworms efficiently to be profitable, says Roberts. Populations of these insects in 2002 were moderate to heavy, he adds.

“Some areas of the state had as intense pressure as I've ever seen. And this was sustained pressure in some areas. Once we got into spraying worms in mid-July, we were in it up until the end of August. We tended to struggle over a more widespread area this past year in attempting to control tobacco budworms.

“A lot of this has to do with our use of pyrethroids. We know we've had pyrethroid resistance in the southwest part of the state, and 1997 was the first year it was documented. We saw control problems in other areas this past year, such as in central Georgia. One reason for this is because we had more pressure.

“If you're achieving 50 to 60 percent control with a treatment, and you're treating populations of 10 to 15, you still don't have high enough populations to get through. This year, we were putting sprays on counts of 30 to 50 worms. And if we got 50 percent control, we had a real problem.”

In areas where growers struggled with using pyrethroids on tobacco budworms, Tracer and Steward insecticides did a good job when properly timed, says Roberts. Bt varieties also held up well against tobacco budworms, he says.

“Something we've re-learned is that once we miss tobacco budworms, we'll spend a lot of money trying to play catch-up, and we won't do a good job controlling these large worms. That takes us back to insecticide selection. Once we're dealing with tobacco budworms, we have to look at products such as Steward and Tracer to prevent the threat of resistance.

“We must know our target, and this is where having an experienced scout is helpful. If we're dealing with tobacco budworms, the choices will be Steward or Tracer on non-Bt cotton. If we're dealing with corn earworms, pyrethroids are the most effective products.”

There are three generations of tobacco budworms — early June, July and August, notes the entomologist. There typically are two generations of corn earworms.

Resistance management, says Roberts, is becoming increasingly important for Georgia cotton producers. “The labels on some of these products will tell you not to use them on successive generations. We've talked about pyrethroid resistance, but we need to manage resistance for all of our products. For example, if you use Tracer, you don't need to use it again in August. We need to rotate to another class to manage resistance. We want these products to be efficacious for a long time to come.”

Some Georgia growers saw a resurgence of beet armyworms this past year, he says, primarily in the eastern part of the state. Damaging infestations were seen on seedling cotton in late May and early June.

“These infestations tended to linger throughout the season in these affected areas, and we had other flare-ups. But we have more tools for managing beet armyworms than we once had. And we need to remain conscious of the importance of using natural controls in managing beet armyworms.”

Aphids continue to be a problem for Georgia growers, says Roberts, and there are several products that do a good job of managing these pests. “We have yet to show a consistent yield response to controlling aphids, but we do have effective products.”

Stink bug pressure was sporadic in Georgia in 2002, he says. “We walked fields in June and early July and found a lot of brown stink bugs in our system. Based on our observations and research from Louisiana, it doesn't appear that stink bugs are damaging pre-bloom cotton.

“In attempting to control stink bugs, growers need to be especially careful about not damaging beneficial insects on conventional cotton. We still like to see pyrethroids used for controlling stink bugs, especially early in the season. Pyrethroids also help us control worms.”

Growers in Tift and Colquitt counties and other areas near Albany saw problems this past year with silverleaf whiteflies, says Roberts. The best method for managing this pest is through cultural practices such as avoiding late planting and conserving beneficial insects.

“The growth regulator Knack still is our most consistent treatment on silverleaf whiteflies. The difficulty is knowing when to make that application.”

Roberts expects Bt cotton acreage to increase in some areas of Georgia in 2003, as many growers are asking how much Bt acreage they should plant.

“What is the status of the tobacco budworm in your area? And, more specifically, what about pyrethroid resistance. We think pyrethroid resistance is possible anywhere in the state where tobacco budworms are found, and definitely in the southwest part of Georgia.

“When deciding on how much non-Bt or conventional cotton to plant, make sure you have an experienced scout. And make sure you can be timely with your sprays. You need to be able to spray or cover your non-Bt acres in three days, and you may need multiple applications.”

Growers remember how to fight insects in most situations, says Roberts, but many of them don't have the time and labor to be good insect managers. “Bt cotton is insurance against high insect control costs. And it can be expensive managing tobacco budworms.”